I'm assuming you have already found out that the credentials are root:root, but may not be aware that the user is disabled from SSH login.

You can enable the root user for SSH in /etc/ssh/sshd_config (do a Google search if you need instructions) but it is not advisable to leave this option enabled for any production system.

You'd be better off logging in as root using a physical keyboard, then install sudo, and add your regular user (freebsd:freebsd by default) to the sudoers file. Again, a little searching in Google and you'll be able to find all the info you need to do this.